These vertical pressure vessels are common offshore, in order to keep them upright designers will set them on a stand which we call a skirt. Inside the skirt is the bottom head of the vessel and a drain line. If there is going to be an internal corrosion failure on the vessel, there’s a 90% chance that it will be on the bottom head or the drain. So most integrity management plans call for routine wall thickness assessment of this area. Some get it others don’t!